1. Field of the Invention
This invention relates to a control system for operation of a fluid torque converter for vehicles which is capable of transmitting power from an engine output shaft to a turbine shaft connected to a driving wheel by a fluid transmission operation in a speed change region, and connecting the engine output shaft to the turbine shaft directly in a clutch-operating region.
2. Description of the Prior Art
A fluid torque converter is designed to transmit power generated by an engine from a pump wheel connected to an engine output shaft to a turbine wheel connected to a turbine shaft by a fluid transmission operation. During a fluid transmission operation, slipping necessarily occurs between the pump wheel and turbine wheel which results in a decrease in the transmission efficiency. In order to improve the transmission efficiency, the pump wheel and turbine wheel are connected together directly with a hydraulic or centrifugal direct-coupling clutch to shift the fluid transmission operation to a mechanical transmission operation. The direct-coupling clutch is designed in such a manner that it is usually actuated when the vehicle is running at a comparatively high speed, for example, when the transmission is in the highest position. When the direct-coupling clutch is in a coupled state, the transmission system receives a shock caused by the sudden acceleration or deceleration of the engine. This undesirably deteriorates the driving condition.